Use frequency-based cooperative caching method for multi-layer network structures (e.g. 5g)

ABSTRACT

A method for caching most-frequently requested contents by users in a multi-layer network structure in a bottom layer of a network, wherein the bottom layer of the network includes access points and base stations and for providing a fastest access to files by changing a node connected by a user by performing a content-based handover by directing the user to a point comprising a requested content, wherein the method is based upon a concept of storing files, wherein the files are in high demand in a geographical region, in a cached manner on a basis of cooperation between the base stations that are in juxtaposition to one another. In the method, a group of close-proximity nodes are grouped, and the group of close-proximity nodes ensured to perform user handover therebetween.

CROSS REFERENCE TO THE RELATED APPLICATIONS

This application is the national stage entry of InternationalApplication No. PCT/TR2019/051240, filed on Dec. 29, 2019, which isbased upon and claims priority to Turkish Patent Application No.2018/21380 filed on Dec. 31, 2018, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The inventive method relates to a collaborative caching model formulti-layer network structures. Accordingly, frequently used contentsare kept in the cache at various layers of the network and are presentedto user without moving upwardly the entire network path. The inventivemethod offers a novel solution for which content will be stored at whichpoint and for which of those paths will be selected, in case there aremultiple paths when presenting the stored content to the user.

BACKGROUND

The problem of being unable to rapidly transfer data to users has beenthe subject of many studies for a long time. For that purpose, thecaching method are tried to be used in various manners, however apermanent result could not be provided. In this context, relateddocuments are as follows so as to provide a better understanding of theinvention.

The US patent numbered U.S. Pat. No. 5,944,780 discloses a cachingmethod for network structures. This patent is of importance in terms ofbeing one of the first and primary applications in the caching subject.Accordingly, the online node reports the contents in its cache to thecenter and when these contents are requested, firstly it is checkedwhether the local network comprises the node keeping this content, if itis available, the user is directed to this node. There is neitherinformation nor recommendation for where the cache will be kept, how theuser is going to reach this cache and similar subjects.

The US patent numbered U.S. Pat. No. 9,948,742 discloses a system thatdetermines contents to be cached in user at service provider sides. Thiscaching is for user himself/herself and cannot be shared with anyone. Itis not considered a similar with the inventive method, since it does notprovide a recommendation for collaborative caching and contentdistribution.

The US patent application numbered US2018069751 discloses a cachingsystem for objects stored on a cloud, however it cannot provide asolution since it does not offer a recommendation for use frequency andcollaborative caching. Moreover, it is silent on where the cache will bekept. Since it does not present a recommendation for which node willhold which content, it is not regarded as similar with the inventivemethod.

In the PCT application numbered WO2016165524, response to http-basedcontent request of the user should be sent by base station, if suchinformation is available in the base station. However, there is neitherinformation on a collaborative caching between base stations nor amethod for a content allocation to caches.

In the PCT application numbered WO2017108070, it is foreseen a cache formicro base stations and to present files kept in the cache for use byway of fragmenting files as well as to present them in a fragmentedmanner. It provides neither solution in terms of many aspects nor arecommendation for a collaborative caching.

In the Canadian patent application numbered CN106028400, it is discloseda distributed mechanism applied in base station. Accordingly, if thecontent request is unavailable, there is a loss. The gain resulting fromsaving this content in the cache is calculated, then it is recommendedto cache in case the gain is more than the loss. However, performingsuch calculations in base station cause various technical problems.Furthermore, since it is not possible to reach the use speed achievedwith a collaborative caching by means of these methods, it is notconsidered as similar with the inventive method.

In the European patent application numbered EP2750447, it is foreseen toaccelerate data transfer on the mobile network by means of a handovermechanism. Accordingly, the content is cached at certain border nodes ina close proximity to base stations. In case of a base station change dueto signal attenuation, the closest base station is picked amongcandidate base stations and user is directed to this base station.However, it is not considered as similar with the inventive method,since it does not provide any recommendation for locating the contentsconsciously and by considering the possible handovers and for performinga handover to the base station comprising the content, even though thepresent base station has a very good signal.

In the PCT application numbered WO2017063670, a macro base stationfragments the available files and distributes these fragments to microbase stations connected with itself. It is herein the aim to minimizethe background payload. This optimization is carried out according topopularity of the files. It is known that this invention also can befound in various non-patent publications. The inventive performs a codedcaching for energy efficiency. Said document foresees that the file isdecomposed into different fragments and saved in a coded manner in theform of decomposed fragment. Here, there occurs various technicalproblem at the coding and then caching point, and it can be given as anexample for a collaborative caching. However, it is obvious that it isnot referred to content-based handover of base stations throughout thedocument. It relates to a solution for a technical problem similar tothe problem that the inventive method, however it provides absolutelydifferent solution. The above-mentioned invention does not provide agrouping-based solution as the inventive method does.

In the PCT application numbered WO2017152486, it is disclosed a cacheseparated into different hierarchical levels. Accordingly, even thoughit is foreseen a content popularity-based caching, this is distributedvertically. Accordingly, while it is foreseen that contents consideredas the most popular are at the closest level (base station) to user, itis foreseen that less popular contents should be upper layers of thenetwork. Herein, it is not possible to refer to a collaborative cachingand horizontal orientation.

SUMMARY

The inventive method is a method for caching the most-frequentlyrequested contents by users in a multi-layer network structure in thebottom layer of the network (e.g. access points, base stations) and forproviding the fastest access to files by way of changing the nodeconnected by user by performing a content based handover by means ofdirecting user to the point that comprises the requested content,wherein the inventive method is based upon the concept of storing fileswhich are in high demand in a geographical region, in a cached manner onthe basis of cooperation between base stations that are in juxtapositionto one another. In the inventive method, a group of close-proximitynodes are grouped, and it is ensured to perform user handovertherebetween. It is not necessary to know or predict contentpopularities in advance so as to implement this method.

Technical Problem

The procedure performed normally in multi-layer networks is as follows;when user request a content, every network layer directs the user to thedirection comprising the content at an upper layer and ensures to followa path that ends at the server where the content is kept. Thus, userrequest the content from server and the content returns by following thesame (or similar, in rare occasions) path between each layer. Thismethod is the main reason of the limit in the content supply speed.Since this method also is a multi-layer structure, content request andsupply speed are determined by the slowest one of those layers.Particularly, that the multi-later network structures are stuck atcertain points results in the decrease of speed of use. Furthermore, italso leads to a great number of requests waiting to be requested beforethe server a great number of empty files waiting to be sent. Theproblem, to which the inventive method brings a solution, is the problemwith moving a long path. Instead of that, a technical solution ispresented for a technical problem by means of caching the contentrequested in great numbers from the same nodes at the lower levels ofthe multilayer network structure and directing the user to the nodes towhich the content is cached.

Solution to Problem

Nowadays, users request data over certain platforms and users that arein a close distance geographically request the same content repeatedly.This results from a number of reasons and leads to a traffic, of whichmagnitude increases exponentially in the network structure. Every userfirstly is directed to the bottom level station, then is directed to theupper layers by connecting one by one, he/she reaches the servercontaining the file as a result of those directions and requests for therelated content and said content generally returns through a path withan equal length and reaches to the user again. For example, if a contenthaving a great importance for a community (e.g. crowd in a stadium) isdesired to be watched for ten thousand times through wirelesscommunication paths, ten thousands of request reaches to the station,herein they are directed between network layers and then to the servercontaining the content, ten thousand of responses received go throughnetwork layers from the server and distributed to users over basestation. The content mentioned in this example may be a video file, aninternet site file (html or php), a picture file, a voice file, a filewith different format or a mixture thereof.

Upon the population of particularly use of mobile internet nowadays, thenumber of such contents increase day by day, users request similarcontents in great numbers, and they increase the traffic payloadsometimes up to the troublesome points to handle. Popular news is readby millions in a short time, video contents are requested by millions ofusers and popular images are viewed millions of people. A significantamount of those views is carried out in geographically limited locationsand frequency of views sometimes increases in a short period of times atsome points.

Even though there are some caching applications to solve this problempractically, these are called as web cache in the internet architecture.Generally, they are applications oriented to solve the traffic problemaccumulated before the server and an application is not observed, whichperforms a caching at the border of the network.

To this end, the inventive method offers a caching application with afive main features; accordingly, said five features are as follow;grouping the access points, co-operating the caching at the groupedaccess points, triggering the handover according to the state of theavailable content, performing a cache management without preliminaryinformation or prediction on the content popularity and fillingfragments according to certain rules by fragmenting the cache at anaccess point into different fragments. Thus, it provides a faster use bydecreasing the traffic in peak times and intensive regions.

It is necessary to perform a number of arrangements and calculations tocarry out the caching without popularity information in the first place;accordingly, it is required to define and use a hit rate. Said hit ratecorresponds to information of use of the cached information.Accordingly, the hit rate defines the use rate of the cache and measuredthrough the rate of the request provided by the cache to the totalrequest. As the hit rate increases, the number of links to be connectedwith the content server within the network arrangement decreasesaccordingly. The inventive method is divided into four phases forproviding a better understanding thereof. There is a CollaborativeCaching Entity (CCE) that manages the process for triggering phasetransitions. CCE itself also performs caching at the same time.

Phase 0 is a state where every user is connected to the closest accesspoint. As an example, for this case, a wireless network is given that isconnected to the base station providing the best services to the userbefore employing the inventive method. In case user requests a content,there are two cases; in the first case, if the requested content iscached at the access point, it is delivered directly to user from theaccess point. In the second case, the request unavailable in the cacheof the access point is delivered to the content server over CCE and theresponse received is delivered to the user. The new information going tothe access point from the server is subjected to the caching algorithmand then it is decided according to the result whether it would becached or not. The evaluation or result thereof is decided on the accesspoint by employing said algorithm. CCE, at this stage, directs thecontent request received from the access point to the content server andwhen the signal “the cache converged” is given from all access points,it is instructed to proceed the next phase. The cache convergence meansthat contents of the cache is stabilized and do not changesignificantly. Access points are able to measure whether their owncaches converge or not.

Every user at the phase 1 is able to connect to every access point inclose according to the state of content. Access points detect and deleteless popular contents in their caches. Herein, the content is directlydeleted from the cache depending on the request of the content in apredefined time periods in determining the popularity. In case userrequests a content at this point, the requested content is directlydelivered to the user in case it is available in the cache at the accesspoint connected. Otherwise, the request is delivered to CCE. At thisstage, in case there is a request from any access point, CCE checkswhether the content is available at another access point close to theuser. If it is available, the user triggers the handover to the accesspoint comprising the content from the present access point and therequest is directed to the related access point. If the contentrequested by the user from the access point are unavailable at relatedaccess points, the content in the cache of CCE is directed to the accesspoint. If the content is not available in CCE, then it is requested fromthe content server. The caching algorithm is triggered for the newcontent and it is cached or not according to the result of the cachingalgorithm. If CCE memory is full or converged, the access points areinstructed to proceed to Phase 2.

Phase 2 substantially is triggered when CCE cache is full or about tofull. Accordingly, every user is able to connect to every close accesspoint. In case user requests a content, one of those two solutions arefollowed; if the content is found in the cache at the access pointconnected, it is directly directed to the user. If not, the request isdelivered directly to the content server over CCE and the contentreceived from the content server is delivered to the user. The newcontent is cached or not according to the content caching algorithm. AtCCE side, order of the processes are as follow: If a content isrequested over a access point, the handover process is triggered and thecontent is directly directed to the user from the access point by takingover the user by the related access point, in case the content isavailable at another access point around the user. If the content cannotbe found at any of the related access points and available on the cachein CCE, it is directed to the user over the access point from the cacheof CCE. If the content is also unavailable in CCE, it is supplied fromthe content server and is cached or not according to the cachingalgorithm. When the hit rate of CCE falls below a predetermined value,it is instructed to proceed to Phase 3.

When Phase 3 is proceeded, every user is able to connect to the accesspoint closest to him/herself. If user requests a content, the content isdirectly directed to the user if it is available at the access pointconnected. If not, the request is delivered to CCE. Furthermore, theaccess point reports the hit rate to CCE in a predetermined frequencymanner. If an access request is made to CCE, the following processes areperformed on CCE; if the content is available at another access pointclose to user, the handover process is triggered and the user istransferred to the related access point and the content is directlydirected to the user. If the content cannot be found at the relatedaccess points and is available in CCE, the content in the cache of CCEis delivered to the content access point. In the content is not found inCCE, the content is obtained through the server and the new content iscached or not according to the caching algorithm. At this point, if thehit rate of CCE have exceeded a predetermined certain rate according tothe hit rate of the access points, it is instructed to proceed to Phase0.

Hence, the inventive method defined with four phases in a cycle mannerforesees a method for delivering the content requested by the user bypassing fewer layers by way of managing each access point, CCEs to whichsaid access points are connected and caches thereof and for keeping anumber of contents in the cache so as to perform this. The importantpoint is here that the inventive method performs this by cycling shortquestions without turning the network into a closed network. While useris able to reach every content that he/she request on the internetwithout causing an additional delay, he/she also is able to reach thedata available in the cache. To this end, it turns the access points inan area into a group, manages them by means of CCE and carries the userto the access point comprising the data by means of handover in case therequested data is available in the cache.

Definitions of some term and abbreviations used in the description forproviding a better understanding of the inventive method are as follow;the first point in which user connects to the network in a multi-layernetwork structure. Said access point on the mobile network is defined asbase station. The second layer to which said base stations are connectedare internet service suppliers. The third layer is defined as servers towhich the internet service suppliers are connected. Herein, the numberof said layers may be increased easily by those skilled in the art, whennecessary; for example, internet service suppliers already work withmultiple layers in itself. Said process array may be operated easily byadding new phases for a network model comprised of four or more layers.In this case, that the intervening elements have caches as the number oflayers increases is that user makes the most use of the cache byperforming a handover on lower layers. For example, in a four-layerstructure, the handover process is maintained such that it is performedat the first, second and third layer and a layer is added to theflowchart given in the accompanying Figures. This process can beperformed easily by those skilled in the art.

The expression “the access point close to user” refers to the accesspoint giving the strongest signal to the user, not the physicalproximity. In general, though these two concepts are synonymous, it isappropriate to use a signal-based evaluation due to the advantageprovided in the state of the art. The handover process is thetransmittance of a user to an access point from another. This process isa commonly used process in the art when triggered by the geographicalfield or signal quality. Accordingly, when user connects to an accesspoint and when user disconnects to an access point after a definedcommunication between two access points and user, he/she connects to theother simultaneously. This process is a common method used in the stateof the art due to various reasons, for example, user moving whileconnected to mobile network connects to a base station giving a strongersignal when the signal supplied by a station weakens and simultaneouslydisconnects to the base station previously connected.

The inventive product gathers a group of access point as a group bymeans of performing the above-mentioned four-phase method and carriesout a collaborative caching among them. It also introduces the cache ofan upper network layer into said collaborative caching and thus, offersthe requested content in a multi-layer network swiftly. In case thenetwork comprises more layers, the same procedure is performed simplystarting from the bottom to uppers and again groups and caches amongthem are created, tests are performed to determine whether the contentis available, those available in the cache are presented to user andrequests for those unavailable in the cache are delivered to an upperlevel, thereby providing a collaborative caching.

Another feature of the inventive method is to operate independently fromthe caching algorithm. According to social preferences, location (e.g.stadium) and other variables, user skilled in the art may use differentcaching algorithms or may alter caching algorithms used previously.Herein, it is sufficient for the caching algorithm to make a choice andto output this choice. The inventive method is absolutely free atdeciding whether a content is cached or not. It is recommended in thestate of the art that those who are skilled in the art choose analgorithm considering the request rates.

Advantageous Effects of Invention

Thus, the inventive method is offered as a collaborative caching method,wherein access points are group, user handover is triggered according tothe state of the available content, the cache management is performedwithout any preliminary information on content popularity profiles andthe cache at an access point may be fragmented into different fragments.Thus, both access speed of user to the content is increased and it isevaluated as a result of simulations that the multi-layer traffic willbe reduced significantly

BRIEF DESCRIPTION OF THE DRAWINGS

Disclosure of drawings annexed in the description is as below;

FIG. 1 illustrates a diagram of fragmental cache concept. Accordingly,the cache is fragmented and then used, and it is graphically showed thatfragment in which every file is located should be free from each other.Since that the most popular content is in a portion of every cache andother contents are in other portions stands out as the most effectivemethod, it is recommended such fragmenting. Accordingly, every contentis in a simple cache, thereby providing the possibility to perform acontent change in base station in the group swiftly.

FIG. 2 illustrates an example for two-layer use. Accordingly, every userconnects to the network over the first level. There are caches at boththe first level and second level and also shown with the drawing.

FIG. 3 illustrates an example for multi-layer network. Accordingly, thefirst level cache service group connects to the network over a networkgateway. Service is provided here for data on the cache on this networkgateway and provided for those unavailable over the second level. Eachof users are connected to the network over a single service point andthey can be transmitted to other service points that they can connect,when necessary.

FIG. 4 illustrates an example of the flowchart, wherein access pointsare performed for two-stage cache. Accordingly, the caching algorithmfirstly controls the device converges contents for the first level cacheor not. Accordingly, the first level cache proceeds to the second levelcache, waits depending on whether it converges or not or proceeds to thecaching algorithm 3. Afterwards, it controls CCE and returns if it isnot fallen to a proper threshold. If it is fallen to a proper threshold,it closes new requests for caching and controls the cache hit rate andreturns to the initial point, if it exceeds a certain rate.

FIG. 5 illustrates a diagram of processes that CCE performs for thetwo-stage cache. Accordingly, if the first level cache has converged thedevice contents, the caching algorithm is activated and controls whetherthe second level caches are converged or not. Accordingly, it closes thecaching for new files and controls CCE. If hit rate of CCE is fallen toa proper threshold, the caching algorithm is activated again and returnsand controls the previous step until the hit rate of CCE is fallen belowa certain rate. After it is fallen, it returns to the initial point andperform the process likewise.

FIG. 6 illustrates a general view of the recommended algorithm.Accordingly, the processes to be carried out in the first and secondlevel caches are shown. Even though an illustration for a second levelis preferred in terms of a better description, this is one of theembodiments of the inventive method. It is obvious that the inventivemethod comprises characteristic applicable for network structures withdesired levels. Level numbers in the examples provided throughout thedescription are provided for an exemplary illustration and constitute nolimitation. For example, the process array given in this drawing may beeasily implemented for a three-level network.

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What is claimed is:
 1. A method of using a network layer cache forcaching in multi-layer network structures of fifth-generation (5G),defining a cyclical process comprising the following steps: a.controlling whether a requested content is available in a memory of abase station, when a user requests a content; b. delivering the contentby fulfilling a request through the base station in case the requestedcontent is available in a first level cache; c. transmitting the requestto a content server over a Collaborative Caching Entity (CCE) anddelivering a received response to the user in case the requested contentis unavailable in the first level cache; d. introducing a new file intoa caching algorithm, caching the new file or not according to a resultof the caching algorithm; e. continuing a process of step (d) until thefirst level cache converges; f. deleting a least requested one of filesin the first level cache after a warning “a cache converged”; g.transmitting the request to the CCE in case of a content request by theuser, wherein the CCE detects whether there is an access point close tothe user; when there is the access point close to the user, detectingwhether a requested file is available at the access point or one ofaccess points; when the requested file is available at the access pointor one of the access points, performing a handover of the user to arelated base station; h. controlling a cache of the CCE in case therequested content is unavailable in the cache close to the access point,when the requested content is available, delivering the requestedcontent over the access point connected by the user; when the requestedcontent is not available, requesting the content from the content serverand introducing the requested content into the caching algorithm whilepresenting for the user; caching the requested content or not accordingto the result of the caching algorithm; i. controlling a cache of theaccess point in case of the request by the user, when the cache of theCCE is full; directing the cache of the CCE directly to the user whenthe cache of the CCE is available in the cache of the access point;checking whether the content is available in another access point aroundthe user when the content is not available in the cache of the accesspoint; performing the handover and transmitting the user to a relatedaccess point when the cache of the CCE is not available; j. controllingthe cache of the CCE when the cache of the CCE is unavailable insurrounding caches of the access points; transmitting over the accesspoint connected by the user when the access point is available in thecache of the CCE; requesting the content from the content server anddelivering to the user when the access point is not available in thecache of the CCE; k. controlling the cache of the access point when ahit rate of the CCE falls below a predetermined value and the userrequests the content; directing the content directly to user when thecontent is available in the cache of the access point; controllingcaches of neighboring base stations when the content is not available;transferring the user to the related base station, when the user isavailable in the caches of the neighboring base stations; delivering thecontent request to the CCE and controlling the cache of the CCE when theuser is not available in the neighboring base stations; transmitting tothe cache of the related access point when the content request isavailable in the cache of the CCE; requesting from the content serverand introducing into the caching algorithm in case the content requestis not available in the cache of the CCE and caching the content requestor not according to the result of the caching algorithm; returning to aninitial point when the hit rate of the CCE falls below the predeterminedvalue.